The invention relates to a method for producing book blocks composed of folded printed sheets, wherein the printed sheets having different print images are supplied separately according to a specific sequence to the sewing apparatus of a thread stitching machine and are stitched to one another by at least one twine which extends through the fold of the printed sheets.
Methods of this type serve to produce books of a high binding quality.
The various folded printed sheets forming the book blocks are made available in stacked form in multiple copies in a specific sequence according to the contents of the book block to be produced and they are fed one after the other through a separating apparatus onto a processing section.
On the way to the sewing apparatus of the thread stitching machine, which, as is known, is configured of different sewing systems, the printed sheets run through a station in which they are checked for correctness and processing readiness. For the processing in the sewing apparatus, they are opened upstream of this station and fed in astride manner to a saddle-shaped support where they are taken over by carriers of a circulating conveying arrangement.
A reading apparatus, which is directed at the saddle-shaped support from the outside determines which printed sheet is involved which is subsequently checked in a comparison apparatus connected to the reading apparatus. The comparison apparatus signals to a control if a sheet is faulty. If this is the case, the processing process is stopped and the faulty printed sheet is replaced. The comparison apparatus comprises the data of the desired values for the printed sheets destined for a complete book block as well as on their sequence; the required data are picked up or stored in a preceding calibration process.
This manner of recognizing the printed sheets makes it possible to ensure the sequence of the printed sheets and the correctness.
The recognition of whether the folded printed sheets are opened correctly before they are transferred to the stitching process remains unsolved. The result of an incorrectly opened printed sheet would be that it is only partially grasped in the sewing process and subsequently not anchored in the bound book block. It does occur that a printed sheet is not opened in the center before it is deposited on the saddle-shaped support so that only a portion of the inner fold edges is resting on the stitching saddle or only a portion of the folds is grasped during the sewing. The printed sheets which were not grasped sit loosely between the bound printed sheets; thus, a book turns out to be useless.